<template>
<div class="list">
  <ul>
    <li class="item"
        v-for="item  of letters"
        :key="item"
        @click="handleLetterClick"
        @touchstart="handleTouchStrart"
        @touchmove="handleTouchMove"
        @touchend="handleTouchEnd"
        :ref="item">
      {{item}}
    </li>
  </ul>
</div>
</template>

<script>
export default {
  name:'CityAlphabet',
  props:{
    cities:Object
  },
  computed:{
    letters(){
      const letters=[]
      for(let i in this.cities){
        letters.push(i)
      }
      return letters
    }
  },
  data (){
    return{
      touchStatus:false,
      startY:0,
      timer:null
    }
  },
  updated (){
    this.startY=this.$refs['A'][0].offsetTop
  },
  methods:{
    handleLetterClick(e){
      //触发事件
      this.$emit("change",e.target.innerText)
      //console.log(e.target.innerText)
    },
    handleTouchStrart(){
      this.touchStatus=true
    },
    handleTouchMove(e){
      if(this.touchStatus){
        if(this.timer){
          clearTimeout()
        }
        this.timer= setTimeout(()=>{
          const touchY= e.touches[0].clientY
          const  index = Math.floor((touchY-this.startY)/20)
          if ( index >= 0 && index < this.letters.length)
          {
            this.$emit("change",this.letters[index])
          }
        },16)


      }
    },
    handleTouchEnd(){
      this.touchStatus=false
    }
  }
}
</script>


<style scoped>
.list{
  display: flex;
  flex-direction: column;
  justify-content: center;
  position: absolute;
  right:0;
  top:1.58rem;
  bottom:0;
  width:.4rem;

}
  .item{
    line-height:.4rem;
    text-align:center;
    color:#666;
  }
</style>
